In airplanes, there are computers that are powered by a three-phase alternator that is driven by the engine of the airplane.
The alternator is connected to the computer by a power supply device performing control of the pulse width modulation (PWM) type.
The device has a control stage and a power stage. The control stage receives a setpoint signal and supplies the power stage with a control signal that is modulated with a predetermined duty ratio. The power stage is connected firstly to the alternator via a filter and a rectifier, and secondly to the remainder of the computer to which the power stage supplies a voltage that corresponds to the control signal. For this purpose, and by way of example, the power stage includes at least one chopper transistor controlled by the control signal. A regulation loop is provided to guarantee the performance required by the computer (in terms of accuracy and response time).
In this application, where failure of a computer could have consequences that are considered as being critical, one of the main preoccupations is that of detecting failures, and preferably of identifying faulty components.
It is thus known to detect a failure on the basis of a voltage measurement performed on each phase of the alternator, with a zero voltage on one particular phase revealing a failure of that phase, for example. It is also possible to reveal seven types of failure (three types of individual failure, three types of simultaneous failure in two phases, and one type of failure that applies to all three phases simultaneously). This does indeed make it possible to detect the faulty phase, but it does not make it possible to identify the type of failure, i.e. a phase being short circuited to ground, a short circuit between phases, or an open circuit in a phase.